Incorporation of modeling and experimentation for understanding the forming characteristics, instability mechanisms, and quality assessment of micro tubes manufactured via free bending technology

Microtubes play a crucial role in sustainability by enhancing energy efficiency, promoting resource conservation, and supporting eco-friendly technologies across various industries. Their lightweight, high-strength-to-weight ratio, and precision flow control make them vital in medical, aerospace, automotive, and renewable energy applications, aligning with the Sustainable Development Goals (SDGs) by promoting sustainable industrial innovation (SDG 9) and responsible material utilization (SDG 12). One of the crucial factors affecting the quality of microtubes is the size effect, as it influences their structural integrity, flow capacity, and overall performance in various applications. Thus, this study aims to examine the impact of the size effect on the formability and quality of microtubes. First, a micro-theoretical analysis considering grain size was performed to understand the deformation behavior and instability. Afterward, finite element modeling and experimental validation of the free bending forming (FBF) process were conducted to verify the theoretical analysis results. The results showed that formability decreases as the tube diameter and grain size decrease. However, the formability of the microtube is enhanced when the grain size is increased to the extent that only surface single crystals exist in the direction of the wall thickness. Finally, a comparison was made between the microfilament-filled and microtubes. Micro-filament filling effectively increases the microtubes' resistance to instability, improves their formability and forming quality, and reduces defects such as cross-section distortion and variations in wall thickness.